Outdoor grilling systems which utilize infrared radiant energy for cooking are known in the art. The beneficial results which these systems are capable of providing over conventional convective grills are also well known. However, a continuing need exists for better and/or lower cost alternative infrared grills and burner systems which provide greater thermal efficiencies and other improvements.
By way of example, but not by way of limitation, a need exists for better and/or lower cost alternative infrared grills and burner assemblies which:                require less metal for fabrication;        are less complex and are easier and less costly to fabricate and produce;        provide better segregation of cooking zones such that the carryover of heat from one cooking zone to other cooking zones which are not in operation, or are operating at a lower settings, is significantly reduced;        are not limited solely to use with an infrared cooking grate for infrared cooking but also provide the option of alternatively using a convective grate for convective cooking.        
A preferred prior art box burner assembly for use in an infrared grill is disclosed in United States Patent Application Publication No. US 2009/0202688 A1. FIG. 16 of the published application is across-sectional view of the simplest version of the prior art box burner which comprises: a single-walled rectangular firebox; a large diameter burner tube which extends longitudinally through the rectangular firebox and has two rows of flame ports such that flames are ejected in substantially horizontal directions from both sides of the tube burner; and two rows of secondary air openings provided through the bottom of the rectangular box. The two rows of secondary air openings run parallel with the tube burner on each side thereof and are spaced laterally outward from the tube burner a significant distance for feeding the two rows of horizontally flames ejected in opposite directions from the burner tube.
An alternative version of the prior art box burner is depicted in FIG. 4 of the Publication No. US 2009/0202688 A1 wherein; sloped baffles which extend inwardly as far as the two rows of secondary air openings are positioned inside of the rectangular burner box; a layer of insulation is added to the interior wall of the rectangular box beneath the baffles; and the effective width of the burner element is further increased significantly by adding a baffle housing arrangement outside of the large burner tube. As explained in the publication, combustion gasses from the burner also flow into the spaces formed beneath the internal baffles so that the entire volume of the rectangular box must be filled with and heated by the combustion gasses produced by the burner element. The sloped baffles operate to more effectively direct the infrared radiant energy emitted from the interior surfaces of the burner box toward the cooking grate.
A third embodiment of the prior art box burner is shown in FIG. 17 of Publication No. US 2009/0202688 A1. The version of FIG. 17 employs a single-walled firebox which is similar to the single-walled rectangular box of FIG. 16 except that the single-walled box of FIG. 17 has a trapezoidal cross-sectional shape comprising: a wide horizontal bottom plate which includes and extends beyond the rows of secondary air openings on each side of the burner element; a top opening which is wider than the bottom plate; and sloped sides which extend upwardly from the outer edges of the bottom plate to the top of the burner box. The single-walled trapezoidal burner utilizes a wide burner element of the type shown in FIG. 4 comprising a large baffle housing assembly which surrounds the large diameter burner tube.
Based solely upon the illustration of the trapezoidal firebox in FIG. 17, it appears that the total combustion gas receiving volume of the single-walled trapezoidal burner box shown would be about 75% of the volume of a hypothetical rectangular firebox of equal depth and of equal discharge area width and length (i.e., a hypothetical rectangular firebox traced over the illustration of the trapezoidal firebox in FIG. 17).
However, it is important to note that the tracing of a hypothetical rectangular firebox over FIG. 17 is not relevant to any attempt to compare the intended or necessary volume of the trapezoidal box of FIG. 17 to the intended or necessary volumes of the rectangular boxes of FIGS. 4 and 16. Publication No. US 2009/0202688 A1 does not show or discuss any such hypothetical rectangular box and does not teach that the depth and discharge dimensions of the trapezoidal box are, or even could be, the same as those of the single-walled rectangular box shown in FIG. 16 or the baffled rectangular box shown in FIG. 4. Nor does the publication state or suggest, in any other way, that the construction and dimensions of the trapezoidal burner can or should be such that the volume of the trapezoidal firebox would be somewhat less than that of the rectangular burner of FIG. 16 or the rectangular burner of FIG. 4.
Consequently, Publication No. U.S. 2009/0202688 A1 neither discusses nor suggests that any relevant differences actually exist between the actual volumes or operating characteristics of the fireboxes of FIGS. 4, 16, and 17. Rather, by requiring that combustion gases must also fill the volume beneath the sloped internal baffles of FIG. 4, the publication indicates that the total effective volumes and related operating characteristics of all of the rectangular and sloped burners shown in these figures are equalized. Those in the art would readily understand that the depth and the width of the trapezoidal firebox of FIG. 17 can be set as necessary to provide essentially the same volume and operating characteristics as a rectangular box of the type shown in FIG. 4 or 16.
Although the box burner assemblies of US 2009/0202688 A1 are superior to other prior art burners for infrared grilling, the large interior volumes which they require, along with other requirements and characteristics of these burners, present difficult barriers for achieving further improvements in performance and efficiency. Moreover, even if the actual volume of the trapezoidal box of FIG. 17 of the publication were assumed to be somewhat smaller, the performance of the single-walled trapezoidal burner box would still be roughly the same as the performance of the single-walled rectangular firebox shown in FIG. 16. Although a somewhat smaller volume of the trapezoidal firebox might tend toward some increase in the temperature of the combustion gas exiting the top of the trapezoidal firebox, any tendency to provide a higher firebox temperature would be significantly diminished by the large excess volume of cold secondary air which enters the bottom of the firebox through the two rows of air openings. Two rows of air openings providing a sizable total air intake must be provided in the bottoms of the trapezoidal and rectangular boxes of FIGS. 16 and 17 in order to support the two long flame rows extending down the opposite sides of the elongate burner element.
Moreover, any significant reduction in the actual constructed volume of the trapezoidal burner assembly shown in FIG. 17 of Publication No. US 2009/0202688 A1 would also result in other operational and certification problems. According to Boyle's law, at given fuel rate, a significant reduction in volume would produce a corresponding increase in firebox pressure. Although such a significant increase in pressure would then in turn theoretically result in an increased operating temperature in the firebox (Gay-Lussac's law), the increased pressure would also prevent a sufficient amount of secondary air flow into the firebox to complete the combustion process. Therefore, the fuel rate to the firebox would have to be reduced significantly in order to meet industry certification requirements related to carbon monoxide emissions.
Unfortunately, however, such a reduction in the fuel rate for the trapezoidal burner of FIG. 17 would also lead to further problems. Given the fuel supply pressure and rate necessary to support the two long flame rows extending along opposite sides of the elongate burner element used in the assembly, a reduction in the fuel gas supply rate and pressure sufficient to address the CO emission problems caused by the reduced air intake would, in turn, render the burner element susceptible to failing industry wind certification tests which require that the burner must remain lit, with the grill cover open, when exposed to a wind speed of 10 miles per hour (per ANSI standard, 2.23 of ANSI Z21.58-2007).